White elastomer seal materials and a process for manufacture thereof

ABSTRACT

A highly durable, high whiteness elastomer seal material molded from a composition comprising a perfluoroelastomer and a white pigment and having a surface with a whiteness of at least 90 as expressed by a W (Lab) color expression system under the conditions of a 2 degree field of view and a C-light source.

FIELD OF THE INVENTION

The present invention relates to a seal material which is suitably usedin an apparatus where the seal section thereof is irradiated withinfrared light such as in an apparatus using infrared light such as aheat source in a semi-conductor industry or the like, an apparatus wherethere is a secondary infrared light generation because of use at a hightemperature of 600° C. or higher, specifically to a highly durable sealmaterial which has excellent heat resistance and chemical resistancealong with a minimal rise in temperature when irradiated with infraredlight.

The present invention relates to a process for manufacturing a whiteelastomer seal material.

DESCRIPTION OF THE PRIOR ART/RELATED ART

Elastomers such as silicon rubber and nitrile rubber have heretoforebeen widely used as seal materials. In particular, because of theirexcellent heat resistance and chemical resistance, fluoroelastomers areused as seal materials in automobile, aircraft, space explorationdevices, industrial machinery, semi-conductor manufacturing equipment,and the like. Perfluoroelastomers are suitably used as seal materials insemi-conductor manufacturing equipment, because they have particularlyoutstanding heat resistance and chemical resistance. Seal materialscomprising fluoroelastomers or perfluoroelastomers compounded with metaloxides have also been developed for improved plasma resistance,including white seal materials. For example, WO-A-9719983 disclosesperfluoroelastomer compositions which can be effectively used in theprocessing conditions found in dry process semiconductor manufacturingenvironments. These perfluoroelastomer compositions are substantiallyfree of elemental carbon and contain selected metallic reinforcingfillers and titanium dioxide which provides a certain degree ofwhiteness to the cured articles resulting from the compositions.

However seal materials which are used under environments which may beirradiated with infrared light suffer from the likelihood of degradationdue to a rise in the surface temperature of the seal material. None ofthe prior art materials used have yet been able to solve the problem ofthe seal material undergoing degradation under such environments.

SUMMARY OF THE INVENTION

Under such circumstances, an object of the present invention is toprovide a highly durable seal material which has excellent heatresistance and chemical resistance along with a minimal rise intemperature when irradiated with infrared light.

Another object of the present invention is to provide a process formanufacturing a white elastomer seal material wherein the process hasenhanced productivity.

Specifically, the invention is aimed at providing a high surfacewhiteness seal material and a process for manufacture thereof.

The present invention resides in the discovery that enhancing thewhiteness of the seal material surface enables the rise in the surfacetemperature of the seal material to be suppressed when the material isirradiated with infrared light, and the inventors' further continuedintensive study has led to the finding that a seal material having awhiteness of at least 90 as expressed by a W (Lab) color expressionsystem under the conditions of a 2° field of view and a C-light sourceis accompanied by a minimal rise in temperature when irradiated withinfrared light.

In the first aspect of the present invention, a white elastomer sealmaterial is molded from a composition comprising a perfluoroelastomerand a white pigment in an amount at least 3% by weight based on theweight of the composition and having a surface with a whiteness of atleast 90 as expressed by a W (Lab) color expression system under theconditions of a 2° field of view and a C-light source.

In the second aspect of the present invention, a process formanufacturing a seal material having a surface with a whiteness greaterthan 75 as expressed by a W (Lab) color expression system under theconditions of a 2° field of view and a C-light source comprises moldinga seal material from a composition comprising a perfluoroelastomer and awhite pigment in an amount of at least 1% by weight based on the weightof the composition and dipping the molded seal material in aqueoushydrogen peroxide solution for a time sufficient to increase the initialwhiteness of the white elastomer seal material by at least 5 units.

In the third aspect of the present invention, a process formanufacturing a seal material having a surface with a whiteness greaterthan 75 as expressed by a W (Lab) color expression system under theconditions of a 2° field of view and a C-light source comprises moldinga seal material from a composition comprising a perfluoroelastomer and awhite pigment in an amount of at least 1% by weight based on the weightof the composition and irradiating the molded seal material withultraviolet light for a time sufficient to increase the initialwhiteness of the white elastomer seal material by at least 5 units.

In the fourth aspect of the present invention, a process formanufacturing a seal material having a surface with a whiteness greaterthan 75 as expressed by a W (Lab) color expression system under theconditions of a 2° field of view and a C-light source comprises moldinga seal material from a composition comprising a perfluoroelastomer and awhite pigment in an amount of at least 1% by weight based on the weightof the composition and exposing the molded seal material to ozone for atime sufficient to increase the initial whiteness of the white elastomerseal material by at least 5 units.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the relationship between the whitenessand the percent infrared reflectance of perfluoroelastomer surfaces.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The seal material of this invention is molded from a compositioncomprising a perfluoroelastomer and at least 3% by weight of a whitepigment based on the weight of the composition.

Perfluoroelastomers, unlike partially fluorinated elastomers, contain nochemically-degradable carbon-hydrogen bonds in parts of the main polymerchain so that a whitening method in addition to adding a white pigmentcan be applied, which can enhance the whiteness of the seal materialsurface as expressed by a W (Lab) color expression system to a levelgreater than 75, preferably of at least 80, more preferably of at least90.

The compositions of the present invention are based onperfluoroelastomers. By “perfluoroelastomers” it is meant hereinelastomeric perfluoropolymers, that is, substantially fully fluorinatedfluoropolymers which, when cured, exhibit an elastomeric character. Theperfluoroelastomers contain copolymerized cure site monomers that renderthe polymers crosslinkable.

Perfluoroelastomers are polymeric compositions having copolymerizedunits of at least two principal perfluorinated monomers. Generally, oneof the principal comonomers is a perfluoroolefin, while the other is aperfluorovinyl ether. Representative perfluorinated olefins includetetrafluoroethylene and hexafluoropropylene. Suitable perfluorinatedvinyl ethers are those of the formula

CF₂═CFO(R_(f′))_(n)(R_(f′)O)_(m)R_(f)  (I)

where R_(f′) and R _(f″) are different linear or branchedperfluoroalkylene groups of 2-6 carbon atoms, m and n are independently0 -10, and R_(f) is a perfluoroalkyl group of 1-6 carbon atoms.

A preferred class of perfluoro(alkyl vinyl) ethers includes compositionsof the formula

CF₂═CFO(CF₂CFXO)_(n)R_(f)  (II)

where X is F or CF₃, n is 0-5, and R_(f) is a perfluoroalkyl group of1-6 carbon atoms. A most preferred class of perfluoro(alkyl vinyl)ethers includes those ethers wherein n is 0 or 1 and R_(f) contains 1-3carbon atoms. Examples of such perfluorinated ethers includeperfluoro(methyl vinyl) ether and perfluoro(propyl vinyl) ether. Otheruseful monomers include compounds of the formula

CF₂═CFO[(CF₂)_(m)CF₂CFZO]_(n)R_(f)  (III)

where R_(f) is a perfluoroalkyl group having 1-6 carbon atoms, m=0 or 1,n=0-5, and Z=F or CF₃. Preferred members of this class are those inwhich R_(f) is C₃F₇, m=0, and n=1.

Additional perfluoro(alkyl vinyl) ether monomers include compounds ofthe formula

CF₂═CFO[(CF₂CFCF₃O)_(n)(CF₂CF₂CF₂O)_(m)(CF₂ )_(p)]C_(x)F_(2x+1)  (IV)

where m and n=1-10, p=0-3, and x=1-5. Preferred members of this classinclude compounds where n=0-1, m=0-1, and x=1.

Examples of useful perfluoro(alkoxy vinyl) ethers include

CF₂═CFOCF₂CF(CF₃)O(CF₂O)_(m)C_(n)F_(2n+1)  (V)

where n=1-5, m=1-3, and where, preferably, n=1.

Mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl)ethers may also be used.

Preferred perfluoroelastomers are composed of tetrafluoroethylene and atleast one perfluoro(alkyl vinyl) ether as principal monomer units. Insuch copolymers, the copolymerized perfluorinated ether units constitutefrom about 15-50 mole percent of total monomer units in the polymer.

The perfluoropolymer further contains copolymerized units of at leastone cure site monomer, generally in amounts of from 0.1-5 mole percent.The range is preferably between 0.3-1.5 mole percent. Although more thanone type of cure site monomer may be present, most commonly one curesite monomer is used. Suitable cure site monomers includenitrile-containing fluorinated olefins and nitrile-containingfluorinated vinyl ethers. Other cure site monomers include olefinsrepresented by the formula R₁CH═CR₂R₃, wherein R₁ and R₂ areindependently selected from hydrogen, fluorine, bromine and iodine andR₃ is independently selected from hydrogen, fluorine, bromine, iodine,alkyl, and perfluoroalkyl. The alkyl group may be substituted with oneor more halogen atoms. The perfluoroalkyl group may contain up to about12 carbon atoms. However, perfluoroalkyl groups of up to 4 carbon atomsare preferred. In addition, the cure site monomer preferably has no morethan three hydrogen atoms. Examples of such olefins include ethylene,vinylidene fluoride, vinyl fluoride,4-bromo-3,3,4,4-tetrafluorobutene-1, 4-iodo-3,3,4,4-tetrafluorobutene-1,trifluoroethylene, 1-hydropentafluoropropene, and2-hydropentafluoropropene.

Useful nitrile-containing cure site monomers include those of theformulas shown below.

CF₂═CF—O(CF₂)_(n)—CN  (VI)

where n=2-12, preferably 2-6;

CF₂═CF—O[CF₂—CF(CF₃)—O]_(n)—CF₂—CF(CF₃)—CN  (VII)

where n=0-4, preferably 0-2;

 CF₂═CF—[OCF₂CFCF₃]_(x)—O—(CF₂)_(n)—CN  (VIII)

here x=1-2, and n=1-4; and

CF₂═CF—O—(CF₂)_(n)—O—CF(CF₃)CN  (IX)

where n=2-4.

Those of formula (VIII) are preferred. Especially preferred cure sitemonomers are perfluorinated polyethers having a nitrile group and atrifluorovinyl ether group. A most preferred cure site monomer is

CF₂═CFOCF₂CF(CF₃)OCF₂CF₂CN  (X)

i.e. perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) or 8-CNVE.

The perfluoroelastomers suitable for use in the present invention maycontain any of a variety of end groups as a result of the use of varyinginitiators or chain transfer agents during polymerization. For example,the polymers may contain sulfonate, sulfonic acid, carboxylate,carboxylic acid, carboxamide, difluoromethyl groups or trifluorovinylgroups.

Any conventional white pigment may be used as the white pigmentcomponent whether organic or inorganic, provided that the white pigmentresults in the whitening effect according to the present invention. Thisspecifically includes titanium oxide, barium sulfate, silicon dioxide, afluororesin such as polytetrafluoroethylene and the like. Titaniumdioxide is especially preferred. The white pigment is incorporated atleast in an amount of 1% by weight, preferably 3% by weight based on theweight of the composition. A level below 1% by weight will notcompletely whiten the surface layer of the sheet material to which thewhitening treatment of this invention is carried out, failing to providea white seal material.

The sealing material of the present invention will generally include acompound which is capable of crosslinking the perfluoroelastomer, forexample an organotin compound or certain amino group-containing benzenecompounds. Suitable organotin compounds include allyl-, propargyl-,triphenyl- and allenyl tin curatives. Tetraalkyltin compounds ortetraaryltin compounds are the preferred curing agents for use inconjunction with nitrile-substituted cure sites. The amount of curingagent employed will necessarily depend on the degree of crosslinkingdesired in the final product as well as the type and concentration ofreactive moieties in the perfluoroelastomer. In general, about 0.5-10parts per hundred parts rubber, i.e. phr, of curing agent can be used,and 1-4 phr is satisfactory for most purposes. It is believed that thenitrile groups trimerize to form s-triazine rings in the presence ofcuring agents such as organotin, thereby crosslinking theperfluoroelastomer. The crosslinks are thermally stable, even attemperatures of 275° C. and above.

A preferred cure system, useful for perfluoroelastomers containingnitrile-containing cure sites utilizes bis(aminophenols) andbis(aminothiophenols) of the formulas

and tetraamines of the formula

where A is SO₂, O, CO, alkyl of 1-6 carbon atoms, perfluoroalkyl of 1-10carbon atoms, or a carbon-carbon bond linking the two aromatic rings.The amino and hydroxyl groups in formulas XI and XII above, areinterchangeably in the meta and para positions with respect to the groupA. Preferably, the curing agent is a compound selected from the groupconsisting of 2,2-bis[3-amino-4-hydroxyphenyl]hexafluoropropane;4,4′-sulfonylbis(2-aminophenol); 3,3′-diaminobenzidine; and3,3′,4,4′-tetraaminobenzophenone. The first of these preferred curingagents will be referred to as diaminobisphenol AF. The curing agents canbe prepared as disclosed in U.S. Pat. No. 3,332,907 to Angelo.

Diaminobisphenol AF can be prepared by nitration of4,4′-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]bisphenol (i.e.bisphenol AF), preferably with potassium nitrate and trifluoroaceticacid, followed by catalytic hydrogenation, preferably with ethanol as asolvent and a catalytic amount of palladium on carbon as catalyst. Ofthe members the preferred class, a particularly referred compound is3,3′-diaminobenzidine.

The level of curing agent should be chosen to optimize the desiredproperties of the vulcanizate. In general, a slight excess of curingagent over the amount required to react with all the cure sites presentin the polymer is used. Typically, 0.5-5.0 parts by weight of thecurative per 100 parts of polymer is required. The preferred range is1.0-2.5 parts.

Additives, such as accelerators, stabilizers, plasticizers, lubricants,fillers, and processing aids typically utilized in perfluoroelastomercompounding can be incorporated into the compositions of the presentinvention, provided they have adequate stability for the intendedservice conditions.

Seal materials comprising elastomer compositions can be molded by knownmethods such as extrusion, compression molding, and the like.

The compositions of the invention may be prepared by mixing theperfluoroelastomer, white pigment, optional curing agent and any othercomponents using standard rubber compounding procedures. For example,the components may be mixed on a two roll rubber mill, in an internalmixer, for example, a Banbury internal mixer, or in an extruder. Thecurable compositions may then be crosslinked (i.e. cured) by applicationof heat and/or pressure. When compression molding is utilized, a presscure cycle is generally followed by a post cure cycle during which thepress cured composition is heated at elevated temperatures in excess of200° C. for several hours.

The surface of the seal material must have a whiteness of greater than75 as expressed by a W (Lab) color expression system under theconditions of a 20 field of view and a C-light source, preferably awhiteness of 80 or higher, more preferably a whiteness of 90 or higher.The higher the whiteness, the greater the extent of suppressing the risein the surface temperature of the seal material when irradiated withinfrared light, the greater the difficulty with which the seal materialwill degrade; a whiteness of 90 or higher can significantly prevent theseal material from degrading.

A seal material having a surface with a whiteness of greater than 75 asexpressed by a W (Lab) color expression system under the conditions of a2° field of view and a C-light source may be obtained by dipping a sealmaterial molded from a perfluoroelastomer and white pigment in aqueoushydrogen peroxide solution. The specific whitening treatment conditionsare suitably selected according to the degree of whiteness required fromamong, the concentration of the aqueous hydrogen peroxide solution, thetemperature of the solution, and the dipping time. Tables 1 and 2 showtypical treatment conditions for a seal material having a surface withat least 80 in whiteness and typical treatment conditions for a sealmaterial having a surface with at least 90 in whiteness, respectively.

TABLE 1 Aqueous hydrogen peroxide About About About 60-80° C. solution,temperature 20° C. 60° C. 60° C. Aqueous hydrogen peroxide 3% 0.1% 1%1-3% solution, concentration Dipping time 90-100 30-40 10-15 8-12 hrshrs hrs hrs Whiteness W (Lab) 80-89 80-89 80-89 80-89

TABLE 2 Aqueous hydrogen peroxide About About About solution,temperature 60° C. 80° C. 80° C. Aqueous hydrogen peroxide 4% 3% 10%solution, concentration Dipping time 96 hrs 72 hrs 48 hrs Whiteness W(Lab) 90- 90- 90-

A seal material having a surface whiteness of greater than 75 asexpressed by a W( Lab) color expression system under the conditions of a20 field of view and a C-light source can also be obtained byirradiating a seal material molded from a composition comprising aperfluoroelastomer and a white pigment with UV light. Specific whiteningtreatment conditions are suitably selected according to the degree ofwhiteness required in terms of the UV light wavelength and irradiationtime.

For example, a seal material having a surface with a whiteness ofgreater than 75 can be prepared by irradiating a molded seal materialwith UV light at a wavelength not longer than 300 nm for 1 hour at roomtemperature in a chamber. A seal material having a surface with at least90 in whiteness can be obtained by irradiating a molded seal materialwith UV light at a wavelength not longer than 300 nm for three hours atroom temperature in a chamber.

A seal material having surface whiteness greater than 75 as expressed bya W (Lab) color expression system under the conditions of a 2° field ofview and a C-light source may also be obtained by exposing a sealmaterial molded from a composition comprising a perfluoroeleatomer and awhite pigment to ozone. Other whitening methods fail to give a sealmaterial having a surface with at least 95 in whiteness as expressed bythe W (Lab) color expression system under the conditions of a 2° fieldof view and a C-light source, but an exposure to ozone at aconcentration of 3% for about 12 minutes in a chamber at a temperatureof 180° C. can bring the whiteness of the seal material surface to 95 orhigher.

The ozone may be in gaseous form or it may be an aqueous ozone solution,preferably containing 10% ozone in gas or 50 ppm ozone in an aqueoussolution.

Specific whitening treatment conditions are suitably selected accordingto the required whiteness in terms of the ozone concentration, the innerchamber temperature, and the ozone exposure time. However, thetemperature within the chamber must not be higher than the temperaturelimit for the heat resistance of the perfluoroelastomer used. Generally,this will be between 200° C. and 320° C. The treatment time can beshortened by an exposure to both UV light and ozone.

TABLE 3 Chamber internal room 20° C. 20° C. 180° C. 180° C. temperaturetemp. Ozone 3% 3% 10% 3% 3% concentration Ozone exposure Approx. 30 min20 min 8 min 12 min time 5 min Whiteness W (Lab) 80-89 90-94 90-94 90-9495-

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present invention to itsfullest extent. The following specific embodiments are to be construedas illustrative, and not as constraining the remainder of the disclosurein any way whatsoever.

EXAMPLES

In the following examples, all parts are by weight unless otherwiseindicated.

W (Lab) Color Expression System

Whiteness, W (Lab), was determined on a Nippon Denshoku IndustriesCompany Limited Model SZ-Sigma 80 Color Measuring System. In thissystem, reflection of Commission Internacional de L'Eclairage (CIE)White Light Source C was measured from the rubber parts. The resultingCIELab values were then converted to W (Lab) using the formula W(Lab)=100−[(100−L)²+a²+b²]^(½). A W (Lab) value of 100 is perfectlywhite, while a value of 0 is perfectly black.

Examples 1-2 and Comparative Examples 1-3

The polymer used in the examples was a terpolymer having copolymerizedunits of 56.2 wt. % tetrafluoroethylene, 43 wt. % perfluoromethylperfluorovinyl ether, and 0.8 wt. % 4-bromo-3,3,4,4-tetrafluorobutene-1.The polymer was mixed with the following additives to form a curablecomposition.

Polymer 100 parts by weight Titanium dioxide 20 parts by weight ProtonSponge ™ 0.5 parts by weight Trimethylallylisocyanurate 2.0 parts byweight Luperco ™ 101-XL 3.0 parts by weight

Luperco™101-XL is a mixture of (2,5-dimethyl-2,5-bis(t-butyl)hexane and45% inert ingredients. Proton Sponge is 1,8-bis-(dimethylamino)napthalene, commercially available from Aldrich Chemical Company.

The compounded polymer was molded into a perfluoroelastomer sheet whichwas cured at 200° C. for 15-20 minutes and post cured in an air oven at288° C. for 24 hours.

Disc sample pieces 25 mm in diameter were fabricated from the curedsheet.

The surface of the test piece was whitened under the conditions given inTable 4. Table 4 shows the whiteness of the surface of each test pieceas expressed by a W (Lab) color expression system under the conditionsof a 2° field of view and a C-light source.

A whitened test piece was mounted on a device with 10 a large samplechamber unit MPC-3100 attached to a spectral photometer, UV-3100,manufactured by Shimazu Seisakusho and was illuminated with light at awavelength given in Table 4, thereby measuring % reflectance of eachtest piece. The results are given in Table 4 and FIG. 1.

TABLE 4 Percent Percent Percent reflectance reflectance reflectanceOzone or Chamber at at at H₂O₂ internal Irradiation Whiteness wavelengthwavelength wavelength Concentration temperature time W (Lab) 750 nm 1000nm 1250 nm Ex. 1 3% OZONE 180° C. 30 97 86.43% 85.73% 83.70% minutes Ex.2 3% OZONE 180° C. 8 94 79.32% 77.48% 77.56% minutes Comp. 3% 80° C. 1084 70.48% 73.49% 74.43% Ex. 1 H₂O₂ hours Comp. 1% 80° C. 10 82 67.82%71.75% 73.28% Ex. 2 H₂O₂ hours Comp. 10% 20° C. 8 78 61.72% 66.68%69.37% Ex. 3 H₂O₂ hours

A test piece surface having a whiteness of at least 90 has a highpercent reflectance, making it possible to prevent a rise in surfacetemperature. As the whiteness reaches 95, the reflectance becomesconsiderably high so that seal materials having a whiteness 95 orhigher, will serve particularly fittingly in environments where the risein the surface temperature of infrared irradiated seal materials is anissue.

Example 3-6

The polymer used in the examples was a terpolymer having copolymerizedunits of 56.2 wt. % tetrafluoroethylene, 43 wt. % perfluoromethylperfluorovinyl ether, and 0.8 wt. % 4-bromo-3,3,4,4-tetrafluorobutene-1.The polymer was mixed with the following additives to form a curablecomposition.

Polymer 100 parts by weight Titanium dioxide 20 parts by weight ProtonSponge ™ 0.5 parts by weight Trimethylallylisocyanurate 2.0 parts byweight Luperco ™ 101-XL 3.0 parts by weight

Luperco™ 101-XL is a mixture of (2,5-dimethyl-2,5-bis(t-butyl)hexane and45% inert ingredients.

Proton Sponge is 1,8-bis-(dimethylamino) napthalene, commerciallyavailable from Aldrich Chemical Company.

The compounded polymer was molded into a perfluoroelastomer sheet whichwas cured at 200° C. for 15-20 minutes and post cured in an air oven at288° C. for 24 hours.

A dumbbell shaped #3 specimen was prepared as a test piece in accordancewith JIS K6250 and K6251 dated 1993, using the cured sheet.

The resultant test pieces were dipped in 3% aqueous hydrogen peroxidesolution at 80° C. for given time intervals listed in Table 5, afterwhich the whiteness was calculated. Tensile strength and elongation atthe break according to JIS K 6250 dated 1993, were also measured. Theresults are given in Table 5.

Comparative Example 4

The test piece was prepared in the same manner as that for Example 3-6and the whiteness was calculated for the resultant test piece. Theresult is given in Table 5.

Comparative Example 5

The polymer used in the example was a terpolymer having copolymerizedunits of 55.2 wt. % tetrafluoroethylene, 42.6 wt. % perfluoromethylperfluorovinyl ether, and 2.2 wt. %perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene). The polymer was mixedwith the following additives to form a curable composition.

Polymer 100 parts by weight 18-crown-6 polyether 0.2 parts by weightPolytetrafluoroethylene 2 parts by weight Titanium dioxide 3 parts byweight Tetraphenyltin 2 parts by weight

The compounded polymer was molded into a perfluoroelastomer sheet whichwas cured at 200° C. for 15-20 minutes and post cured under nitrogen at288° C. for 24 hours.

A dumbbell shaped #3 specimen was prepared as a test piece in accordancewith JIS K6250 and K6251 dated 1993, using the cured sheet, and thewhiteness was calculated for the resultant test piece. The result isgiven in Table 5.

TABLE 5 Comp. Comp. Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 4 Ex. 5 White pigment 1616 16 16 16 5 (% by weight) Dipping time 16 40 72 96 0 0 (hours)Whiteness W (Lab) 84 87 90 91 73 35 Tensile strength 147 140 141 135 167— (kgf/cm²) Elongation at the 185 198 208 174 175 — break (%)

A comparison of Examples 3-6 with Comparative Examples 4 and 5 indicatesthat even after being dipped in aqueous hydrogen peroxide solution toimprove the whiteness, the seal materials can maintain their requiredmechanical properties.

Examples 7-11

The test piece was prepared in the same manner as that for Example 3-6.

The resultant test pieces were exposed to ozone at a concentration 3%and/or UV light at wavelengths 185 nm and 284 nm in a chamber for a timegiven in Table 6, and then their whiteness was calculated. Mechanicalproperties were also measured as with Examples 3-6. The results aregiven in Table 6.

TABLE 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ozone No No Yes Yes Yes UV YesYes Yes No Yes Chamber Internal 20 180 20 180 180 temperature (° C.)Ozone and/or UV 180 180 180 180 180 Exposure time (min) Whiteness W(Lab) 88 85 93 97 96 Tensile strength 170 171 172 177 198 (kgf/cm²)Elongation at the break 271 280 275 270 298 (%)

A comparison of Example 8 with Example 10 indicates that the under thesame conditions, exposure to ozone can increase the whiteness more thancan UV irradiation. A comparison of Example 7 with Example 8 suggeststhat the whitening by UV light irradiation is not affected by thechamber internal temperature. A comparison of Example 10 with Example 11demonstrates that whitening by an exposure to ozone under hightemperature conditions can give whiteness no different that which wouldhave been obtained without the combined use of UV light; however, acombined use of ozone along with UV light can result in bettermechanical properties.

Example 12

Sample 12A was prepared by compounding the following components on atwo-roll rubber mill: 100 parts of a terpolymer containing copolymerizedunits of tetrafluoroethylene (TFE), perfluoro(methyl vinyl)ether (PMVE)and 8-CNVE, (weight ratio TFE/PMVE/8-CNVE 48.8/49/2.2), preparedsubstantially according to the general process described in U.S. Pat.No. 5,789,489; 1.5 parts diaminobisphenol AF curative; and 1.03 partstitanium dioxide. Samples 12B, 12C, and 12D were prepared in the samemanner, except that 12B contained 2.07 parts titanium dioxide and 100parts terpolymer, 12C contained 3.14 parts titanium dioxide and 100parts terpolymer, and 12D contained 5.34 parts titanium dioxide and 100parts terpolymer. Slabs of 2-3 mm thickness of the compoundedcompositions were cured in a press at 200° C. for 15-20 minutes and thenpost cured in an air oven at 288° C. for 24 hours. The cured slabs wereexposed to gaseous ozone at a concentration of 10% in a chamber at 200°C. under the conditions shown in Table 7. The degree of whiteness wasdetermined using the W (Lab) color expression system under conditions ofa 2° field of view and a C-light source.

TABLE 7 Sample 12A 12B 12C 12D Initial whiteness 63.4 72.2 74.8 80.2value Whiteness after 15 71.8 85.0 87.4 91.5 minute exposure to ozoneWhiteness after 30 77.1 86.8 88.8 92.3 minute exposure to ozoneWhiteness after 60 78.9 87.8 90.2 93.3 minute exposure to ozone

The present invention has been described in detail with respect topreferred embodiments. Changes and modifications may be made withoutdeparting from the invention in its broader aspects, and it is theintention, therefore, in the appended claims to cover all such changesand modifications as fall within the true spirit of the invention.

What is claimed is:
 1. A white elastomer seal material molded from acomposition comprising a perfluoroelastomer and a white pigment in anamount of at least 3% by weight based on the weight of the compositionand having a surface with a whiteness of at least 90 as expressed by a W(Lab) color expression system under the conditions of a 2° field of viewand a C-light source.
 2. A process for manufacturing a seal materialhaving a surface with a whiteness greater than 75 as expressed by a W(Lab) color expression system under the conditions of a 2° field of viewand a C-light source, wherein the process comprises molding a sealmaterial from a composition comprising a perfluoroelastomer and a whitepigment in an amount of at least 1% by weight based on the weight of thecomposition and dipping the molded seal material in aqueous hydrogenperoxide solution for a time sufficient to increase the initialwhiteness of the white elastomer seal material by at least 5 units.
 3. Aprocess for manufacturing a seal material having a surface with awhiteness of at least 80 as expressed by a W (Lab) color expressionsystem under the conditions of a 2° field of view and a C-light source,wherein the process comprises molding a seal material from a compositioncomprising a perfluoroelastomer and a white pigment in an amount of atleast 3% by weight based on the weight of the composition and dippingthe molded seal material in aqueous hydrogen peroxide solution for atime sufficient to increase the initial whiteness of the white elastomerseal material by at least 5 units.
 4. A process for manufacturing a sealmaterial having a surface with a whiteness greater than 75 as expressedby a W (Lab) color expression system under the conditions of a 2° fieldof view and a C-light source, wherein the process comprises molding aseal material from a composition comprising a perfluoroelastomer and awhite pigment in an amount of at least 1% by weight based on the weightof the composition and irradiating the molded seal material withultraviolet light for a time sufficient to increase the initialwhiteness of the white elastomer seal material by at least 5 units.
 5. Aprocess for manufacturing a seal material having a surface with awhiteness of at least 80 as expressed by a W (Lab) color expressionsystem under the conditions of a 2° field of view and a C-light source,wherein the process comprises molding a seal material from a compositioncomprising a perfluoroelastomer and a white pigment in an amount of atleast 3% by weight based on the weight of the composition andirradiating the molded seal material with ultraviolet light for a timesufficient to increase the initial whiteness of the white elastomer sealmaterial by at least 5 units.
 6. A process for manufacturing a sealmaterial having a surface with a whiteness greater than 75 as expressedby a W (Lab) color expression system under the conditions of a 2° fieldof view and a C-light source, wherein the process comprises molding aseal material from a composition comprising a perfluoroelastomer and awhite pigment in an amount of at least 1% by weight based on the weightof the composition and exposing the molded seal material to ozone for atime sufficient to increase the initial whiteness of the white elastomerseal material by at least 5 units.
 7. A process for manufacturing a sealmaterial having a surface with a whiteness of at least 80 as expressedby a W (Lab) color expression system under the conditions of a 2° fieldof view and a C-light source, wherein the process comprises molding aseal material from a composition comprising a perfluoroelastomer and awhite pigment in an amount of at least 3% by weight based on the weightof the composition and exposing the molded seal material to ozone for atime sufficient to increase the initial whiteness of the white elastomerseal material by at least 5 units.
 8. A white elastomer seal materialmanufactured by the process of any one of claims 2-7.